Updating to new OTS repo from https://github.com/khaledhosny/ots.git

src/gsub.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gsub.h"
 
 #include <limits>
 #include <vector>
 
-#include "gdef.h"
-#include "gpos.h"
 #include "layout.h"
 #include "maxp.h"
 
 // GSUB - The Glyph Substitution Table
 // http://www.microsoft.com/typography/otspec/gsub.htm
 
+#define TABLE_NAME "GSUB"
+
 namespace {
 
 // The GSUB header size
 const size_t kGsubHeaderSize = 4 + 3 * 2;
 
 enum GSUB_TYPE {
   GSUB_TYPE_SINGLE = 1,
   GSUB_TYPE_MULTIPLE = 2,
   GSUB_TYPE_ALTERNATE = 3,
   GSUB_TYPE_LIGATURE = 4,
@@ skipping 44 matching lines @@
 // Single Substitution Subtable
 bool ParseSingleSubstitution(const ots::OpenTypeFile *file,
                              const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
 
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read single subst table header");
   }
 
   const uint16_t num_glyphs = file->maxp->num_glyphs;
   if (format == 1) {
     // Parse SingleSubstFormat1
     int16_t delta_glyph_id = 0;
     if (!subtable.ReadS16(&delta_glyph_id)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read glyph shift from format 1 single subst table");
     }
     if (std::abs(delta_glyph_id) >= num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("bad glyph shift of %d in format 1 single subst table", delta_glyph_id);
     }
   } else if (format == 2) {
     // Parse SingleSubstFormat2
     uint16_t glyph_count = 0;
     if (!subtable.ReadU16(&glyph_count)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read glyph cound in format 2 single subst table");
     }
     if (glyph_count > num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad glyph count %d > %d in format 2 single subst table", glyph_count, num_glyphs);
     }
     for (unsigned i = 0; i < glyph_count; ++i) {
       uint16_t substitute = 0;
       if (!subtable.ReadU16(&substitute)) {
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("Failed to read substitution %d in format 2 single subst table", i);
       }
       if (substitute >= num_glyphs) {
-        OTS_WARNING("too large substitute: %u", substitute);
-        return OTS_FAILURE();
+        return OTS_FAILURE_MSG("too large substitute: %u", substitute);
       }
     }
   } else {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad single subst table format %d", format);
   }
 
   if (offset_coverage < subtable.offset() || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %x", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
   }
 
   return true;
 }
 
-bool ParseSequenceTable(const uint8_t *data, const size_t length,
+bool ParseSequenceTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, const size_t length,
                         const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   uint16_t glyph_count = 0;
   if (!subtable.ReadU16(&glyph_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read glyph count in sequence table");
   }
   if (glyph_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("bad glyph count %d > %d", glyph_count, num_glyphs);
   }
   for (unsigned i = 0; i < glyph_count; ++i) {
     uint16_t substitute = 0;
     if (!subtable.ReadU16(&substitute)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failedt o read substitution %d in sequence table", i);
     }
     if (substitute >= num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad subsitution (%d) %d > %d", i, substitute, num_glyphs);
     }
   }
 
   return true;
 }
 
 // Lookup Type 2:
 // Multiple Substitution Subtable
 bool ParseMutipleSubstitution(const ots::OpenTypeFile *file,
                               const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t sequence_count = 0;
 
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&sequence_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read header of multiple subst table");
   }
 
   if (format != 1) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad multiple subst table format %d", format);
   }
 
   const uint16_t num_glyphs = file->maxp->num_glyphs;
   const unsigned sequence_end = static_cast<unsigned>(6) +
       sequence_count * 2;
   if (sequence_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad segence end %d, in multiple subst", sequence_end);
   }
   for (unsigned i = 0; i < sequence_count; ++i) {
     uint16_t offset_sequence = 0;
     if (!subtable.ReadU16(&offset_sequence)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read sequence offset for sequence %d", i);
     }
     if (offset_sequence < sequence_end || offset_sequence >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad sequence offset %d for sequence %d", offset_sequence, i);
     }
-    if (!ParseSequenceTable(data + offset_sequence, length - offset_sequence,
+    if (!ParseSequenceTable(file, data + offset_sequence, length - offset_sequence,
                             num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse sequence table %d", i);
     }
   }
 
   if (offset_coverage < sequence_end || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
   }
 
   return true;
 }
 
-bool ParseAlternateSetTable(const uint8_t *data, const size_t length,
+bool ParseAlternateSetTable(const ots::OpenTypeFile *file,
+                            const uint8_t *data, const size_t length,
                             const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   uint16_t glyph_count = 0;
   if (!subtable.ReadU16(&glyph_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read alternate set header");
   }
   if (glyph_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad glyph count %d > %d in alternate set table", glyph_count, num_glyphs);
   }
   for (unsigned i = 0; i < glyph_count; ++i) {
     uint16_t alternate = 0;
     if (!subtable.ReadU16(&alternate)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read alternate %d", i);
     }
     if (alternate >= num_glyphs) {
-      OTS_WARNING("too arge alternate: %u", alternate);
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Too large alternate: %u", alternate);
     }
   }
   return true;
 }
 
 // Lookup Type 3:
 // Alternate Substitution Subtable
 bool ParseAlternateSubstitution(const ots::OpenTypeFile *file,
                                 const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t alternate_set_count = 0;
 
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&alternate_set_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read alternate subst header");
   }
 
   if (format != 1) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad alternate subst table format %d", format);
   }
 
   const uint16_t num_glyphs = file->maxp->num_glyphs;
   const unsigned alternate_set_end = static_cast<unsigned>(6) +
       alternate_set_count * 2;
   if (alternate_set_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad end of alternate set %d", alternate_set_end);
   }
   for (unsigned i = 0; i < alternate_set_count; ++i) {
     uint16_t offset_alternate_set = 0;
     if (!subtable.ReadU16(&offset_alternate_set)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read alternate set offset for set %d", i);
     }
     if (offset_alternate_set < alternate_set_end ||
         offset_alternate_set >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad alternate set offset %d for set %d", offset_alternate_set, i);
     }
-    if (!ParseAlternateSetTable(data + offset_alternate_set,
+    if (!ParseAlternateSetTable(file, data + offset_alternate_set,
                                 length - offset_alternate_set,
                                 num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse alternate set");
     }
   }
 
   if (offset_coverage < alternate_set_end || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
   }
 
   return true;
 }
 
-bool ParseLigatureTable(const uint8_t *data, const size_t length,
+bool ParseLigatureTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, const size_t length,
                         const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   uint16_t lig_glyph = 0;
   uint16_t comp_count = 0;
 
   if (!subtable.ReadU16(&lig_glyph) ||
       !subtable.ReadU16(&comp_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read ligatuer table header");
   }
 
   if (lig_glyph >= num_glyphs) {
-    OTS_WARNING("too large lig_glyph: %u", lig_glyph);
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("too large lig_glyph: %u", lig_glyph);
   }
   if (comp_count == 0 || comp_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad component count of %d", comp_count);
   }
   for (unsigned i = 0; i < comp_count - static_cast<unsigned>(1); ++i) {
     uint16_t component = 0;
     if (!subtable.ReadU16(&component)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read ligature component %d", i);
     }
     if (component >= num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad ligature component %d of %d", i, component);
     }
   }
 
   return true;
 }
 
-bool ParseLigatureSetTable(const uint8_t *data, const size_t length,
+bool ParseLigatureSetTable(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length,
                            const uint16_t num_glyphs) {
   ots::Buffer subtable(data, length);
 
   uint16_t ligature_count = 0;
 
   if (!subtable.ReadU16(&ligature_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read ligature count in ligature set");
   }
 
   const unsigned ligature_end = static_cast<unsigned>(2) + ligature_count * 2;
   if (ligature_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad end of ligature %d in ligature set", ligature_end);
   }
   for (unsigned i = 0; i < ligature_count; ++i) {
     uint16_t offset_ligature = 0;
     if (!subtable.ReadU16(&offset_ligature)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read ligature offset %d", i);
     }
     if (offset_ligature < ligature_end || offset_ligature >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad ligature offset %d for ligature %d", offset_ligature, i);
     }
-    if (!ParseLigatureTable(data + offset_ligature, length - offset_ligature,
+    if (!ParseLigatureTable(file, data + offset_ligature, length - offset_ligature,
                             num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse ligature %d", i);
     }
   }
 
   return true;
 }
 
 // Lookup Type 4:
 // Ligature Substitution Subtable
 bool ParseLigatureSubstitution(const ots::OpenTypeFile *file,
                                const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
   uint16_t lig_set_count = 0;
 
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage) ||
       !subtable.ReadU16(&lig_set_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read ligature substitution header");
   }
 
   if (format != 1) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad ligature substitution table format %d", format);
   }
 
   const uint16_t num_glyphs = file->maxp->num_glyphs;
   const unsigned ligature_set_end = static_cast<unsigned>(6) +
       lig_set_count * 2;
   if (ligature_set_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad end of ligature set %d in ligature substitution table", ligature_set_end);
   }
   for (unsigned i = 0; i < lig_set_count; ++i) {
     uint16_t offset_ligature_set = 0;
     if (!subtable.ReadU16(&offset_ligature_set)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read ligature set offset %d", i);
     }
     if (offset_ligature_set < ligature_set_end ||
         offset_ligature_set >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad ligature set offset %d for set %d", offset_ligature_set, i);
     }
-    if (!ParseLigatureSetTable(data + offset_ligature_set,
+    if (!ParseLigatureSetTable(file, data + offset_ligature_set,
                                length - offset_ligature_set, num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse ligature set %d", i);
     }
   }
 
   if (offset_coverage < ligature_set_end || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
   }
 
   return true;
 }
 
 // Lookup Type 5:
 // Contextual Substitution Subtable
 bool ParseContextSubstitution(const ots::OpenTypeFile *file,
                               const uint8_t *data, const size_t length) {
-  return ots::ParseContextSubtable(data, length, file->maxp->num_glyphs,
+  return ots::ParseContextSubtable(file, data, length, file->maxp->num_glyphs,
                                    file->gsub->num_lookups);
 }
 
 // Lookup Type 6:
 // Chaining Contextual Substitution Subtable
 bool ParseChainingContextSubstitution(const ots::OpenTypeFile *file,
                                       const uint8_t *data,
                                       const size_t length) {
-  return ots::ParseChainingContextSubtable(data, length,
+  return ots::ParseChainingContextSubtable(file, data, length,
                                            file->maxp->num_glyphs,
                                            file->gsub->num_lookups);
 }
 
 // Lookup Type 7:
 // Extension Substition
 bool ParseExtensionSubstitution(const ots::OpenTypeFile *file,
                                 const uint8_t *data, const size_t length) {
   return ots::ParseExtensionSubtable(file, data, length,
                                      &kGsubLookupSubtableParser);
 }
 
 // Lookup Type 8:
 // Reverse Chaining Contexual Single Substitution Subtable
 bool ParseReverseChainingContextSingleSubstitution(
     const ots::OpenTypeFile *file, const uint8_t *data, const size_t length) {
   ots::Buffer subtable(data, length);
 
   uint16_t format = 0;
   uint16_t offset_coverage = 0;
 
   if (!subtable.ReadU16(&format) ||
       !subtable.ReadU16(&offset_coverage)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read reverse chaining header");
   }
 
   const uint16_t num_glyphs = file->maxp->num_glyphs;
 
   uint16_t backtrack_glyph_count = 0;
   if (!subtable.ReadU16(&backtrack_glyph_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read backtrack glyph count in reverse chaining table");
   }
   if (backtrack_glyph_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad backtrack glyph count of %d", backtrack_glyph_count);
   }
   std::vector<uint16_t> offsets_backtrack;
   offsets_backtrack.reserve(backtrack_glyph_count);
   for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
     uint16_t offset = 0;
     if (!subtable.ReadU16(&offset)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read backtrack offset %d", i);
     }
     offsets_backtrack.push_back(offset);
   }
 
   uint16_t lookahead_glyph_count = 0;
   if (!subtable.ReadU16(&lookahead_glyph_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to read look ahead glyph count");
   }
   if (lookahead_glyph_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad look ahead glyph count %d", lookahead_glyph_count);
   }
   std::vector<uint16_t> offsets_lookahead;
   offsets_lookahead.reserve(lookahead_glyph_count);
   for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
     uint16_t offset = 0;
     if (!subtable.ReadU16(&offset)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Can't read look ahead offset %d", i);
     }
     offsets_lookahead.push_back(offset);
   }
 
   uint16_t glyph_count = 0;
   if (!subtable.ReadU16(&glyph_count)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Can't read glyph count in reverse chaining table");
   }
   if (glyph_count > num_glyphs) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad glyph count of %d", glyph_count);
   }
   for (unsigned i = 0; i < glyph_count; ++i) {
     uint16_t substitute = 0;
     if (!subtable.ReadU16(&substitute)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to read substitution %d reverse chaining table", i);
     }
     if (substitute >= num_glyphs) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad substitute glyph %d in reverse chaining table substitution %d", substitute, i);
     }
   }
 
   const unsigned substitute_end = static_cast<unsigned>(10) +
       (backtrack_glyph_count + lookahead_glyph_count + glyph_count) * 2;
   if (substitute_end > std::numeric_limits<uint16_t>::max()) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad substitute end offset in reverse chaining table");
   }
 
   if (offset_coverage < substitute_end || offset_coverage >= length) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Bad coverage offset %d in reverse chaining table", offset_coverage);
   }
-  if (!ots::ParseCoverageTable(data + offset_coverage,
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to parse coverage table in reverse chaining table");
   }
 
   for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
     if (offsets_backtrack[i] < substitute_end ||
         offsets_backtrack[i] >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad backtrack offset %d for backtrack %d in reverse chaining table", offsets_backtrack[i], i);
     }
-    if (!ots::ParseCoverageTable(data + offsets_backtrack[i],
+    if (!ots::ParseCoverageTable(file, data + offsets_backtrack[i],
                                  length - offsets_backtrack[i], num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse coverage table for backtrack %d in reverse chaining table", i);
     }
   }
 
   for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
     if (offsets_lookahead[i] < substitute_end ||
         offsets_lookahead[i] >= length) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Bad lookahead offset %d for lookahead %d in reverse chaining table", offsets_lookahead[i], i);
     }
-    if (!ots::ParseCoverageTable(data + offsets_lookahead[i],
+    if (!ots::ParseCoverageTable(file, data + offsets_lookahead[i],
                                  length - offsets_lookahead[i], num_glyphs)) {
-      return OTS_FAILURE();
+      return OTS_FAILURE_MSG("Failed to parse lookahead coverage table %d in reverse chaining table", i);
     }
   }
 
   return true;
 }
 
 }  // namespace
 
-#define DROP_THIS_TABLE \
-  do { file->gsub->data = 0; file->gsub->length = 0; } while (0)
+#define DROP_THIS_TABLE(msg_) \
+  do { \
+    file->gsub->data = 0; \
+    file->gsub->length = 0; \
+    OTS_FAILURE_MSG(msg_ ", table discarded"); \
+  } while (0)
 
 namespace ots {
 
 // As far as I checked, following fonts contain invalid values in GSUB table.
 // OTS will drop their GSUB table.
 //
 // # too large substitute (value is 0xFFFF)
 // kaiu.ttf
 // mingliub2.ttf
 // mingliub1.ttf
@@ skipping 36 matching lines @@
 // KacstArt.ttf
 // KacstPoster.ttf
 // KacstQurn.ttf
 // KacstDigital.ttf
 // KacstBook.ttf
 // KacstFarsi.ttf
 
 bool ots_gsub_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
   // Parsing gsub table requires |file->maxp->num_glyphs|
   if (!file->maxp) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Missing maxp table in font, needed by GSUB");
   }
 
   Buffer table(data, length);
 
   OpenTypeGSUB *gsub = new OpenTypeGSUB;
   file->gsub = gsub;
 
   uint32_t version = 0;
   uint16_t offset_script_list = 0;
   uint16_t offset_feature_list = 0;
   uint16_t offset_lookup_list = 0;
   if (!table.ReadU32(&version) ||
       !table.ReadU16(&offset_script_list) ||
       !table.ReadU16(&offset_feature_list) ||
       !table.ReadU16(&offset_lookup_list)) {
-    return OTS_FAILURE();
+    DROP_THIS_TABLE("Incomplete table");
+    return true;
   }
 
   if (version != 0x00010000) {
-    OTS_WARNING("bad GSUB version");
-    DROP_THIS_TABLE;
-    return true;
-  }
-  if ((offset_script_list < kGsubHeaderSize ||
-       offset_script_list >= length) ||
-      (offset_feature_list < kGsubHeaderSize ||
-       offset_feature_list >= length) ||
-      (offset_lookup_list < kGsubHeaderSize ||
-       offset_lookup_list >= length)) {
-    OTS_WARNING("bad offset in GSUB header");
-    DROP_THIS_TABLE;
+    DROP_THIS_TABLE("Bad version");
     return true;
   }
 
-  if (!ParseLookupListTable(file, data + offset_lookup_list,
-                            length - offset_lookup_list,
-                            &kGsubLookupSubtableParser,
-                            &gsub->num_lookups)) {
-    OTS_WARNING("faild to parse lookup list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_lookup_list) {
+    if (offset_lookup_list < kGsubHeaderSize || offset_lookup_list >= length) {
+      DROP_THIS_TABLE("Bad lookup list offset in table header");
+      return true;
+    }
+
+    if (!ParseLookupListTable(file, data + offset_lookup_list,
+                              length - offset_lookup_list,
+                              &kGsubLookupSubtableParser,
+                              &gsub->num_lookups)) {
+      DROP_THIS_TABLE("Failed to parse lookup list table");
+      return true;
+    }
   }
 
   uint16_t num_features = 0;
-  if (!ParseFeatureListTable(data + offset_feature_list,
-                             length - offset_feature_list, gsub->num_lookups,
-                             &num_features)) {
-    OTS_WARNING("faild to parse feature list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_feature_list) {
+    if (offset_feature_list < kGsubHeaderSize || offset_feature_list >= length) {
+      DROP_THIS_TABLE("Bad feature list offset in table header");
+      return true;
+    }
+
+    if (!ParseFeatureListTable(file, data + offset_feature_list,
+                               length - offset_feature_list, gsub->num_lookups,
+                               &num_features)) {
+      DROP_THIS_TABLE("Failed to parse feature list table");
+      return true;
+    }
   }
 
-  if (!ParseScriptListTable(data + offset_script_list,
-                            length - offset_script_list, num_features)) {
-    OTS_WARNING("faild to parse script list table");
-    DROP_THIS_TABLE;
-    return true;
+  if (offset_script_list) {
+    if (offset_script_list < kGsubHeaderSize || offset_script_list >= length) {
+      DROP_THIS_TABLE("Bad script list offset in table header");
+      return true;
+    }
+
+    if (!ParseScriptListTable(file, data + offset_script_list,
+                              length - offset_script_list, num_features)) {
+      DROP_THIS_TABLE("Failed to parse script list table");
+      return true;
+    }
   }
 
   gsub->data = data;
   gsub->length = length;
   return true;
 }
 
 bool ots_gsub_should_serialise(OpenTypeFile *file) {
-  const bool needed_tables_dropped =
-      (file->gdef && file->gdef->data == NULL) ||
-      (file->gpos && file->gpos->data == NULL);
-  return file->gsub != NULL && file->gsub->data != NULL
-      && !needed_tables_dropped;
+  return file->gsub != NULL && file->gsub->data != NULL;
 }
 
 bool ots_gsub_serialise(OTSStream *out, OpenTypeFile *file) {
   if (!out->Write(file->gsub->data, file->gsub->length)) {
-    return OTS_FAILURE();
+    return OTS_FAILURE_MSG("Failed to write GSUB table");
   }
 
   return true;
 }
 
 void ots_gsub_free(OpenTypeFile *file) {
   delete file->gsub;
 }
 
 }  // namespace ots
 
+#undef TABLE_NAME
+#undef DROP_THIS_TABLE